Combined service and emergency brake system apparatus



J. H. (SLACK Sept. 13, 1966 COMBINED SERVICE AND EMERGENCY BRAKE SYSTEM APPARATUS 7 Sheets-Sheet 1 Filed Dec.

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INVENTOR. JA MES H CLA C K W a W Sept. 13, 1966 J. H. CLACK 3,272,566

COMBINED SERVICE AND EMERGENCY BRAKE SYSTEM APPARATUS Filed Dec. 50, 1955 7 Sheets-Sheet 2 1 INVENTOR.

JAMES HGLAGK MAL Sept. 13, 1966 J. H. CLACK 3,272,566

COMBINED SERVICE AND EMERGENCY BRAKE SYSTEM APPARATUS Filed Dec. 30, 1963 7 Sheets$heet 5 L A l 1 J. H. CLACK Sept. 13, 1966 COMBINED SERVICE AND EMERGENCY BRAKE SYSTEM APPARATUS 7 Sheets-$heet 4 Filed Dec. 30, 1963 Sept. 13, 1966 J. H. cLAcK 3,272,566

COMBINED SERVICE AND EMERGENCY BRAKE SYSTEM APPARATUS Filed Dec. 50, 1963 7 Sheets-Sheet 5 Sept. 13, 1966 J. H. CLACK 33 ,56

COMBINED SERVICE AND EMERGENCY BRAKE SYSTEM APPARATUS Filed Dec. 30, 1963 7 Sheets-Sheet 6 COMBINED SERVICE AND EMERGENCY BRAKE SYSTEM APPARATUS J. H. CLACK Sept. 13, 1966 7 Sheets-Sheet 7 Filed Dec.

FIG. 19

284 255 2&6 2E5 5 United States Patent 3,272,566 COMBINED SERVICE AND EMERGENCY BRAKE SYSTEM APPARATUS James H. Clack, 6145 Buckboard Drive, Rio Linda, Calif. Filed Dec. 30, 1963, Ser. No. 334,505 14 Claims. (Cl. 303-13) This invention relates to brake systems and associated apparatus for wheel supported vehicles and is particularly useful for trucks, trailers, tractors and the like, and is a continuation-in-part of application Serial No. 199,813 for Safety Brake System, and of application Serial No. 267,398 for Combined Service and Emergency Brake System Apparatus.

In the main, in normal service operation, trucks and trailers utilize brakes operated by fluids such as air or hydraulic liquid. Generally, pressure developed by a pump or air compressor is transmitted through appropriate control valves to apply braking forces on the wheels. By and large, these systems have worked well. However, rupture of pressure hoses, diaphragms, or mechanical breakdown of the compressor, pump or a valve have resulted, in the past, in disasters. Therefore, these systems, wherein fluid pressure is used to apply the brakes, oftentimes further employ mechanical brake mechanisms as a back-up for emergency operation. One emergency system includes a cylinder and spring-loaded piston connected in tandem to drive the same brake-shoe driving connection as operated by the fluid system. The spring is restrained by the fluid pressure of the system. When the fluid pressure fails, the spring takes over to operate the driving connection. Thus, the driving connection is powered in service operation by fluid and in emergency operation by the spring. Arrangements of this kind have been referred to in the trade as piggyback units.

Piggyback units necessarily are rather long. Notwithstanding their extended length, however, they can provide only a relatively short throw. A short throw can contribute to the problem of fading wherein, due :to heating, the drums expand so as to place themselves out of reach of the shoes (linings). Furthermore, emergency braking forces applied by large springs have not been entirely satisfactory over an extended life due to their shorter flexing life as compared to smaller springs.

Air equipped systems also possess a seemingly inherent weakness, in that moisture tends to accumulate in the system. Extremely cold weather can cause this moisture to freeze and crucial operating components either will not start to work until thawed or will, even worse, he permanently damaged. Also rust and deterioration through dirt, grit and air-borne pollutants act to an accelerated degree on pneumatic braking systems.

It is generally an object of this invention to provide means for operating the brakes of a wheel supported vehicle in a manner which overcomes the foregoing and certain other problems of prior systems.

It is another object of the invention to provide a simplifled means for applying the brakes to a vehicle in both service and emergency operation.

It is another object of the invention to provide a brake system in which the brakes are operative any time the fluid pressure members are rendered inoperative, thereby providing a fail-safe system.

It is a more particular object of the invention to provide a combination service and emergency brake system wherein energy for advancing the brake shoes to brake applying condition during both service and emergency operation is derived substantially entirely by releasing stored energy from a spring biasing means.

Use of spring forces to apply the brakes of a vehicle is inherently a faster acting approach to a fluid brake system and has a number of other inherent advantages over systems where, for example, pneumatic pressure urges the brakes to brake applying position.

The objective of providing a service brake system using actuators wherein spring forces act to apply the brakes under pneumatic or hydrauli control of the springs raises a number of problems, however. These problems, until now, have virtually relegated the use of springs in this manner to parking brake status.

Large forces must be available. As mentioned, however, springs of smaller size have a more desirable flexing life than the larger sizes and are, therefore, to be preferred. Further, to overcome the problem of fading, the travel of the brake applying lever arm should be capable of moving through a relatively wide angle of displacement to fully rotate the camming element. This requires a rather extended movement of the brake piston, inasmuch as the lever arm must be long enough to apply sufficient braking forces at the wheels using conventional fluid pressures in the system. Thus, the need for the presently used, rather long lever arms, is understandable, but imposes a correspondingly long actuator movement if fading is to be overcome.

In short, to use springs in a service system, among other requirements the springs should have good flexing characteristics under all conditions of temperature and provide a long actuator movement.

In addition, spring generated forces must provide trouble-free maintenance and avoid unsatisfactory diminution of force at full displacement of the actuator.

It is generally considered that helical springs tend to break from fatigue midway between their ends. I have observed, however, that the point of fracture is more properly to be identified with the midpoint between the sprung and unsprung masses that are separated by the springs. Where a single spring separates the two masses, there would appear to be substantially no difference in the point of fracture. Therefore, to develop a long throw for the actuator, I have found the use of tandemly disposed springs, separated by an alignment plate, to be particularly effective.

A further problem encountered in any attempt to utilize spring forces for service braking purposes is that helical springs tend to impart an objectionable twisting to the drive movement of the piston rod. This twisting can cause fracture of the rod if it is held fixed with a clevis. Furthermore, when several springs are used together, this twisting causes buckling or scrambling of the springs thereby impairing proper functioning.

Accordingly, it becomes still further objects of the invention to provide a brake system of the foregoing kind in which these and other problems have been resolved.

These and other objects will be more readily apparent from the following description of a preferred e1nbodiment when taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a fragmentary perspective view showing the general arrangement of a system according to the invention in a typical environment, namely in a truck or tractor member, illustrated in outline;

FIGURE 2 is a diagrammatic illustration of a brake system according to the invention;

FIGURE 3 is a fragmentary view, partially in section of components of the system shown in FIGURE 1, shown in brake off position;

FIGURE 4 is a view comparable to that of FIGURE 3 but with the components in a brake-set position;

FIGURE 5 shows diagrammatically another embodiment of the system, according to the invention;

FIGURE 6 is a side elevation view partly in section of a brake actuator, according to the invention;

FIGURE 7 is a section view along the line 7--7 of FIGURE 6;

FIGURE 8 is an end view along the line 8-8 of FIGURE 6;

FIGURE 9 is a section view along the line 9-9 of FIGURE 6;

FIGURE 10 shows the actuator of FIGURE 6 arranged to pull the brake lever to a brake set position;

FIGURE 11 shows another embodiment of a spring applied brake system;

FIGURE 12 shows a valve actuating means employed in the system of FIGURE 11;

FIGURE 13 shows another embodiment of a valve actuating means as used in the system shown in FIG- URE 11;

FIGURE 14 is a center-line section view of a brake actuating unit according to another embodiment;

FIGURE 15 is a section view taken along the lines 1515 of FIGURE 14;

FIGURE 16 is an end view along a section at lines 1616;

FIGURE 17 is a section view of a portion of the actuator shown in FIGURE 14 in its compressed condition;

FIGURE 18 shows a prior art valve construction;

FIGURE 19 shows another embodiment of a spring applied brake system;

FIGURE 20 schematically shows a simplified embodiment of a brake actuating unit; and

FIGURE 21 schematically shows another simplified embodiment of a brake actuating unit.

' Ordinarily in brake systems, as carried by Wheel supported vehicles having an operators compartment, brake drums are provided including a friction surface. Coacting brake shoes, carrying a friction lining, are arranged for movement into and out of engagement with the friction surface in order to apply and release the brakes. Not uncommonly, an operating member, such as a lever arm, is movable between brake applying and brake releasing positions in order to control the movement of the brake shoes.

In general, brake actuating apparatus has here-in been provided comprising a connecting member operably connected to move the brake shoes between brake applying and brake releasing positions. The apparatus includes a cylinder, a piston within the cylinder, and resilient biasing means disposed to urge the piston with respect to the cylinder in order to advance a connecting member to apply the brakes for both service and emergency operation. The apparatus has been simplified to the point where energy for advancing the connecting member during both service and emergency operation is derived substantially entirely by releasing stored energy from the biasing means. Fluid pressure means, operable from the operators compartment, as by a foot pedal, is arranged for both gradually or substantially instantaneously releasing the stored energy of the biasing means as well as to restore the energy thereof.

The apparatus as above described is adapted for either pneumatic or hydraulic operation. For example, hydraulic operation is shown in FIGURES 1 through 4 wherein the system is generally designated by the reference numeral 12. The system is preferably installed, for example, in a truck or tractor .13, as shown in outline in FIGURE 1. However, its use is equally of value to attendant members, such as a trailer, or in other vehicles which rely on wheels for support and on braking systems for control, such as aircraft.

Many types of hydraulic braking systems exist. All of such systems have in common, a hydraulic reservoir and a pump. The pump, being itself appropriately driven drives hydraulic fluid, under pressure, such as oil, to the various actuating members. In this respect the instant system is no exception.

In other words, any existing or previously known hydraulic service system which includes a pump and reservoir 16, often located in the engine compartment, as in FIGURE 1, can be employed. As is well known in the art, return lines to the reservoir, or sump, are required although such return lines are not shown in FIGURE 1 for greater clarity of disclosure.

The service pump drives fluid, under pressure, to a foot brake or cab control valve 17. Conveniently, valve 17 is linked to the brake pedal 22 and can be of the rotary, four-way variety, with valve and seat dimensions such that the step of going from open to closed or closed to open is a gradual rather than a substantially instantaneous one.

This is to say, that with the vehicle in normal cruising status (i.e., in service operation), valve 17 is in a condition such that substantially the full pressure exerted by pump 16 makes itself felt through the pump service line 18 and through valve 17 to the main service line 19 and thus, to the brake controlling cylinder 21. While immediate full depression of brake pedal 22 is effective to cut off the pressure entirely and permit full, instantaneous flow-back through the return line to the reservoir, an intermediate or partial displacement of the brake pedal will effect only a corresponding partial pressure line blockage and opening of the return line, thus providing smooth partial braking. Rotary valves capable of accomplishing this result are readily available commercially and thus require, it is felt, no detailed description. Comparable remarks apply to certain other valves subsequently described.

The main service line 19 leads into, and under customary conditions, through a stand-by or post'emergency valve 26 located adjacent cylinder 21. While FIGURES 1 and 2 show only a single, main service line entering stand-by valve 26, it will be realized, as stated above, that there is also a separate return or feed-back line leading to the main pump reservoir. This feed-back line is designated in FIGURES 3 and 4 by the reference numeral 19a.

Returning to line 19, it can be seen most clearly in FIGURES 3 and 4, that pressurized fluid in line 19 can make its influence felt in the hydraulic pressure chamber 31, located adjacent the lefthand end of cylinder 21.

FIGURE 3 schematically represents a brake-off situation. Here, the full pressure of line 19, through the normally fully open stand-by valve 26, is exerted through the fluid lfi'lled chamber 31 and against the piston head 33 of a plunger 34 projecting through and beyond the right-hand end of cylinder 21 and terminating in a clevis 36.

A helical spring 37, having a very powerful spring constant is interposed between piston head 33 and the rod end 38 of cylinder 21 and serves to bias piston head 33 in la left-hand direction toward the head end 39 of the cylinder. Appropriate flanges 41 and 42 (see FIG- URES 3 and 4) assist in centering or maintaining spring 37 in proper axia-l alignment.

Under most circumstances, smooth operation of the main cylinder is enhanced by providing on the lefthand end of cylinder 21 an eye-bolt bracket 46 adapted to be pivotally mounted on an adjacent frame or chassis member (not shown) of the vehicle, thus enabling the cylinder to rock slightly to conform to the requirements of the extensible and retractable plunger member 64. In this situation the fluid lines between valve 26 and cylinder 21 would preferably be flexible to accommodate the slightly varying attitude of the cylinder.

Translation of plunger 34 and clevis 36 is reflected in a reciprocating, or rocking movement, of a lever 51 pivotably mounted at one end on clevis 36 and secured at the other end to a conventional cam shaft 52 of any standard vehicle brake mechanism, such mechanism being generally characterized by the reference numeral 56.

The brake mechanism, in known manner, is actuated or deactivated by angular rotation of cam shaft 52 (and cams 53) in one direction or the other. It is, therefore, not believed necessary to further describe the structure and operation in detail except to state that a tension spring 57 connected to brake shoes 58 tends to pull the shoes inwardly toward each other about a pair of anchor pins 59 as a pivot, and thus deactivate or release the brake by separating shoes 58 from the encompassing brake drum. As is known, the brake drum has a friction surface which coacts with the friction lining carried by brake shoes 58. Thus, when oppositely urged by cams 53, the brake shoes are moved to brake applying position whereby the linings engage the friction surface of the drums.

As appears most clearly in FIGURE 3, pressurized fluid from main service line 19 is, under customary cruising conditions, elfective to urge the piston in a righthand direction to overcome the left hand bias of spring 37. As a consequence, spring 37 is compressed and plunger 34, cam shaft 52 and the brake are in off position.

Should pressure in line '19 and chamber 31 drop, however, the urging of spring 67 will drive the plunger to the left and overcome the force of spring 57. Thus, the cam shaft is rotated in an opposite direction such that the brake will be in an on or set position. This situation could occur as a result of many different happenings, the most common, perhaps, being a breakdown of the hydraulic pump or a rupture or leak in the feed lines or valves.

Upon happening of such emergency, the brakes will be set and the vehicle will come to a halt. -It is to be noted that while only one brake cylinder is shown in the figures, in actual practice a number of cylinders will be employed for braking the several wheels of the vehicular equipment, each front wheel would be provided with a cylinder and each axle to the rear of cab 60, including trailer axles, could be provided with a pair of such cylinders.

After the vehicle is stopped the operator may effect such repairs to the system as are possible. I have, therefore, provided a convenient stand-by or post-emergency system which is capable of restoring the cylinders and the attendant mechanism to operative condition.

This stand-by system, generally designated by the reference numeral 61 includes a separate reservoir and pump 62 located in a convenient position such as at one end of the drivers seat (not shown) in cab 60. A hand operated lever 63 enables the operator to build up hydraulic pressure in pump 62 and, by suitable orientation of a valve handle 64, .to transmit this pressure into a stand-by feed line 66 leading through stand-by valve 26 and into chamber 31 of cylinder 21.

As is apparent, valve 64 controls the flow of fluid in both pressure line 6'6 and return line 66a.

Valve 26 serves a somewhat similar purpose in that siutable orientation of the cock '67, determines whether main service pressure and return lines 19, 19a, respectively, on the one hand, or stand-by pressure and return lines 66, 66a, respectively, on the other hand, shall be in operation. In other words, rotation of cock 6'7 cuts out lines 19, 19a at the time lines 66, 66a are cut in, and vice versa. Valve 26 is also capable of turning off all lines in the event of cylinder failure.

Stand by system 61 enables the operator to reactivate the braking system and by pumping by hand, even while driving, he can maintain pressure and drive the vehicle to a repair facility. Should it become necessary to set the brakes while driving under stand-by condition it is only necessary for the driver to reach down with his left hand and rotate valve handle 64 until line 66a is placed in communication with the pump reservoir. Under this condition, the biasing effect of spring 37 will urge piston 6 head 33 in the lefthand direction (see FIGURES 3 and 4) and force fluid outwardly through return line 66a. After braking has been effected the driver turns handle 64 back to service position for cruising and pumps with handle 63 to restore pressure in cylinder 21 and thereby deactivate the brakes.

After the necessary repairs are made, the system is switched from stand-by back to main service.

For run-away or comparable situations, I have provided, at a convenient location in cab 60, an emergency or panic button 71 and an attendant quick-acting high volume bleed valve 72 located in lines 19. Valve 72 is actuated by a Bowden or push wire 73 leading from button 71. Upon hitting button 71, valve '72 immediately commences, and continues, to exhaust fluid to atmosphere, thus quickly dropping pressure in the line and permitting all the actuating springs on all the brakes to set the brakes quickly and fully. Concurrently, valve 72 cuts off further flow from pump 16.

Emergency valve 72 would be of especial use where the driver determines that 'foot valve 17 is not suflicient under the circumstances.

As thus described it will be readily evident that the above system employs a spring biasing means which stores substantially the entire energy for applying brakes in both service and emergency operation. As shown in FIG- URES 5 through 10 a pneumatically operated embodiment of the above system is described wherein pneumatically operated fluid pressure means serve to control release of the stored energy of the spring biasing means, as well as to restore such energy as is expended during braking.

The system, shown generally in FIGURE 5, includes fluid pressure means operable from the operators compartment lfOI both gradually or substantially instantaneously releasing stored energy from the spring biasing means and for restoring the energy. An air pump or compressor unit 75 connects via line 76 and a check valve to discharge into an air tank 77 equipped with a conventional relief valve 78. Tank 77 leads via line 79 to suitable valve means designated generally by the reference numeral 80.

Means 80 serves to connect fluid pressure to brake cylinders )0 or to vent air therefrom gradually or suddenly for both service and emergency operation. Valve means 80, as shown in FIGURE 5, diagrammatically provides the various operations to control brake cylinders and can, of course, be constructed in any suitable manner.

Accordingly, a rotationally movable distribution member 81, responsive to movement of a foot pedal (represented by movement of dashed line 82) carried in the cab of the vehicle, serves either to pressurize or vent the brake cylinders to a selected pressure. Member 31 is formed with a passageway or channel 83 which makes connection between a line 84, which transfers air to and from cylinders 90, and one of several vent lines 86. Between line 84 and member 81 a manifold 35 is provided to extend around a substantial portion of the periphery of the member 81. A number of vents designated 86a, 86b, 36c, etc., are distributed around the housing of member 81 and extend generally radially therefrom. Each vent 86 is provided with a pressure relief means such as units designated 87a, 87b, 870, etc., respectively. Each pressure relief unit 87 is set to relieve brake cylinder air pressure down to a predetermined level and hold the pressure at that level. For example, relief means 87a can be set to relieve air pressure exhausting via vent 86a to a level of 115 p.s.i. Unit 87b can be set to establish a lower air pressure such as p.s.i. In the condition shown, valve means 80 serves to connect compressor 75 via line 79, channel 83, manifold 85 and line 84- to apply fluid pressure to brake cylinders 90. Clockwise rotation of member 81, on the other hand, serves to vent brake cylinder air pressure from line 34 via manifold 85 and channel 83 to any one of vents 86.

As noted above, braking forces for both service and emergency operation are applied at the wheels from the stored energy in the spring biasing means located in cylinders 90, whereby venting air from the cylinders 90 releases the spring .forces. These same spring forces will also act whenever there is partial or complete failure of the air supply. The driver of the vehicle will notice a certain dragging on the brakes and be led to effect repairs. Should failure of the air supply leave the brakes fully applied, it may strand the vehicle in an awkward circumstance. Therefore, means for emergency release of the brakes have been provided.

Means for emergency application of the stored energy in the spring biasing means to move the brake shoes to brake applying position are provided. Thus, if [for any reason, venting of air pressure from cylinders 90 via valve means 80 is ineffective to cause the spring biasing means to apply braking forces at the wheels, a panic button 192 can be pulled. Button 192 is carried in the cab of the vehicle and serves to operate a three-way valve 193. Valve 193 is spring-loaded by spring 194 to a condition whereby line 191 normally leads to brake cylinders 90 via a manifold and manifold connection 195, 196, respectively. Thus, normally, air is directed from manifold 195 to and from each of the vehicles brake cylinders 90 by means of piping 197 connected to each. For emergency operation, valve 193 is provided with a vent 198 exhausting to atmospheric pressure whereby pulling button 192 serves via a Bowden wire connection 189 to move the spool 199 upwardly to connect vent 198 to connection 196, thereby directly venting all brake cylinders 90 quickly to atmospheric pressure.

For post-emergency release of the brakes, a cylinder 88 of compressed gas, such as air or carbon dioxide, is connected to a two-position valve 89 operated by a lever in the cab of the vehicle. Slight rotation of valve 89 serves to couple cylinder 88 to line 191 and at the same time serves to disconnect line 84 from same. Accordingly, fluid pressure from cylinder 88 serves to overcome the spring force and releases the brake shoes.

In normal service operation, movement of foot pedal (82) serves to rotate member 81 to interconnect line 84 via channel 83 to any one of vents 86. Thus, slight clockwise rotation of member 81 serves to release air pressure in the brake cylinders 90 to less than full pressure so as to partially release the stored energy of the resilient biasing means. As this energy is partially released, the brakes are correspondingly applied. Further, clockwise rotation of member 81 serves to connect subsequent vents 86 to drop the air pressure in cylinders 90 as desired for commensurately increased braking. Release of foot pedal (82) serves to return member 81 to the position shown in FIGURE under the urging of any suitable resilient means (not shown). While means 80 is shown as operating by discrete steps, any suitable variable relief means can be employed therefor.

A system employing a fluid pressure signal to control reservoir pressures which in turn develop the forces to operate the brakes is shown schematically in FIGURE 11 as adapted for pneumatic operation, the fluid being compressed air.

The signal air system of FIGURE 11 comprises generally a source of fluid under pressure represented by the arrow 130. A first valve means 140 is disposed between the source of fluid pressure and the brake cylinders of the above type wherein spring forces are employed to urge a brake shoe into brake applying position. The first valve means is operable in one condition to transmit a fluid pressure into the brake cylinders to develop a force sufiicient to overpower the spring biasing means in the brake cylinder. In another condition the first valve means 140 serves to vent fluid pressure from the brake cylinders to release stored energy of the spring biasing means. In order to control operation of the first valve means in varying degree between the first and second condition mentioned above, an actuator [160 is provided which is responsive to, and disposed by, a biasing fluid pressure acting normally to fully condition valve means 140 to its brake releasing condition. A counteracting fluid pressure which can be varied is introduced to the actuator to operate valve means 140 in varying degree to its brake applying condition. Another valve means 240 is provided which is operable from the operators compartment of the vehicle for both gradually and subsubstantially instantaneously varying and directing fluid pressure from source to the actuator to operate the actuator in a corresponding varying degree.

In short, a limited depression of valve means 240 generates a related limited fluid pressure signal which serves to correspondingly reduce pressure in the brake cylinders whereby the energy stored in the brake springs is partially released.

In general, operation of the system shown in FIG- URE 11 proceeds as follows. Fluid pressure from source 130 is applied to a service line 131. Fluid pressure is carried along one branch 132 through a parking and emergency brake control valve 133 described further below. Pressure from branch 132 is applied to yieldingly urge or bias the actuator 160 in a downward direction and also supplies a predetermined pressure to an air receiver tank 134. Tank .134 is protected against any sudden drop in pressure by a check valve 135 on the inlet side. The outlet 136 of tank 134 supplies fluid under pressure to the inlet port 137 of valve means controlled by actuator 160. Under the normal biasing action of the pressure applied to actuator via line 138 valve means 140 is conditioned to pass fluid under pressure from inlet 137 to outlet 139 and subsequently to the brake cylinder via line 197. This fluid under pressure serves to move the piston of the brake cylinder to brake releasing position.

-Means serving to control application of the brakes includes a foot-operated valve means 240 for developing a fluid pressure signal in line 141 to be applied through an inlet 142 whereby the biasing force developed by pressure in line 138 can be partially or fully overcome.

A foot pedal operated valve of known design, such as the Bendix-Westinghouse Corporations Model E2 construction shown in FIGURE 18, can be used to provide a controlled air pressure serving as a fluid pressure signal.

When the brake pedal 200 is pressed down by the drivers foot, force is exerted on the plunger 201, rubber graduating spring 202 and to the piston assembly 203. Vertical movement of assembly 203 serves to modulate or vary the source pressure so as to supply and maintain a selected brake signal air pressure. The signal air pressure can then be directed to control the venting of pressure in the brake actuator units. As the piston assembly 203 moves down, its stem including an exhaust seat 204 closes the exhaust, which is otherwise normally open. As the exhaust closes, the inlet valve 205 moves off its seat. Air pressure from the reservoir then enters gradually via inlet valve 205 and flows out at a selected pressure via delivery ports 206 to supply an air pressure signal to the system.

Assuming a given downward displacement of plunger 201, the signal air will develop and maintain a corresponding pressure. When the air pressure in the cavity beneath the piston and the air pressure which is being delivered via ports 206 equals the mechanical force depressing plunger 201, the piston lifts to close off further incoming air. The exhaust remains closed to prevent loss of the signal pressure established.

Thus, the valve seeks a balanced condition where pressure beneath the assembly 203 equals the effort exerted by the drivers foot. Maximum depression of plunger 201 serves to maintain the inlet valve fully open to deliver reservoir pressure.

If pedal 200 is released, the air pressure beneath the piston assembly 203 moves it upwardly to fully open the exhaust. Air below piston assembly 203 and in lines connected to ports 206 drops accordingly to atmospheric through the exhaust port.

Further explanation of the known valve construction shown in FIGURE 18 is not considered necessary. Identification of certain other elements may, however, be helpful. Thus, the construction includes a roller 209, retainer 210 for rubber spring 202, boot 211, return spring 212, spring 213, exhaust diaphragm 21-4, and a piston retainer cap 215.

Valve means 140 can be of similar construction to valve means 240 described above whereby downward movement of a plunger in varying degree serves to pass .a proportionate pressure through the valve.

One embodiment of actuator 161), and its relationship to a valve means 140, such as the Bendix-Westinghouse Corporations Model E2 construction described above, is shown in FIGURE 12. Generally, the actuator includes .a plunger arranged, whereby under pressure of the fluid source the plunger normally serves to condition valve means 140 to maintain the spring means of the brake cylinder in its fully restored condition. An inlet for applying to the plunger a counteracting fluid signal pressure is provided, either to partially or fully release stored energy of the brake springs, depending upon the degree of operation of foot pedal 200. Thus, the varying degree of signal pressure developed at the inlet correspondingly releases the stored energy of the brake spring means.

In the embodiment in FIGURE 12 the plunger means is arranged to comprise first and second expansible pressure chambers, each having a movable wall. The walls are of different pressure-receiving areas and are movable as a unitary construction between advanced and retracted positions. The pressure-receiving area of the movable wall of the first chamber is less than of the second chamber. A plunger actuator member or connecting rod is movable with the walls. Fluid passage means are provided normally passing fluid pressure from the pressure source into the first fluid pressure chamber to urge the movable walls and the actuator member to its advanced position. The inlet for applying a counteracting fluid signal pressure is disposed to pass fluid pressure into the second expansible chamber under control of valve means 240 to urge the movable walls toward their retracted position.

Particularly, an expansible pressure chamber 145 is defined by the cylinder 143 and piston head 144 movable therein. A second expansible chamber 146 is defined by a cylinder 147 and piston head 148. Heads 144 and 148 are held in fixed spaced relation by an axial rod portion 149. The pressure-receiving face 151 of head 144 provides a pressure-receiving area smaller than the pressure receiving face 152 of head 148. Accordingly, with equal pressure applied to faces 151 and 152, the piston head construction will be moved upwardly to a retracted position defined by an annular shoulder 153 provided by the cylinder block 154. Cylinder block 155 is bolted to block 154 and, if desired, suitable sealing gaskets can be provided therebetween, if considerations is properly given to variation of the stroke of member 156.

Plunger actuator member 156 is screwed axially into the piston head assembly and carried between advanced and retracted positions thereof. At the bottom end of member 156 a cylindrically shaped cup 157 is disposed to contact and depress plunger 201 of value means 140 described above. As previously explained downward depression of plunger 201 serves to transmit fluid pressure from inlet 137 to outlet 139, thereby moving the brake pistons to brake releasing condition. During movement of the piston head assembly between advanced and retracted positions it will be observed that the volume of the dead air space defined between piston head 144 and piston head 148 will correspondingly increase or decrease depending upon the direction of movement of the head 1h assembly. A fluid vent 158, bored through cylinder block 154 and terminating in shoulder 153, is disposed to provide breathing for this dead air space. Furthermore, vent 158 serves to provide access for lubrication of piston heads 144, 148 on the low pressure side of each.

A fluid signal pressure inlet 142 serves to inject a counteracting fluid pressure into chamber 146 to partially or fully overcome a biasing force developed by pressure injected into chamber via line 138. Member 156 can therefore be moved in varying degree to a selected position to control the fluid pressure at outlet port 139.

Another embodiment of the actuator is shown in FIGURE 13 wherein the expansible walls are provided by resilient deformable diaphragms 161, 162 each sealed at is periphery to the wall of its respective expans-ible chamber 163, 164. Chambers 163, 164 are respectively provided by a cylinder block 165, a cylinder block 166 and an intermediate cylinder section 167. Section 167 is formed with a pair of openings 168, 169 bored from opposite faces to provide sealing surfaces to support the back side of each diaphragm 161, 162 and permit flexing thereof. Accordingly, the back surface of each diaphragm is supported around a circumference corresponding to that of its chamber 163, 164. A stem 171 is carried by diaphragms 161, 162 and movable therewith by means of the hexagonal nuts and washers shown. Accordingly application of a fluid bias pressure, via line 138, serves to drive stem 171 downwardly to the advanced position whereas application of a counteracting pressure via inlet 142 serves to provide a counteracting force to move stern 171 in an opposite direction thereby applying the brakes.

A spring is disposed in valve means 140 to urge plunger 201 upwardly when pressure -is relieved from line 138 at times when no counteracting pressure is applied via inlet 142.

Valve means 133 serves to provide a parking and emergency brake function controlled manually from the cab of the vehicle or automatically in response to a pressure drop in the fluid pressure source.

In general, a large capacity valve 133 is disposed upstream of actuator means 160. Valve 133 is positionable whereby in one condition, it transmits a biasing fluid pressure to the actuator. Valve 133, when moved from the position shown in FIGURE 11 serves to quickly relieve the biasing pressure through a vent 172 leading to a loW pressure area such as the outside surroundings. Accordingly, venting bias pressure from line 138 by means of valve 133 serves to permit the spring in valve means 140 to move plunger 201 and actuator means upwardly to its brake applying position.

In order to release the brakes it is necessary to reapply a downward force to actuator means 160. This release movement depends upon provision of a source of fluid under pressure in line 138. Spools 230, 291 of valve 133, when moved to the left as shown in FIGURE 11, connect lines 172 and 138 to vent the bias pressure from valve actuator 160 causing brakes to be applied. Manual control by pulling out the parking knob 292, vents the bias line 138. Service system pressure in line 132 normally serves to restrain spring 293 by a force developed via bleed line 294. When knob 292 is pulled to the park position, 295, pressure from line 132 cannot enter the valve housing 296 and, therefore, spring 293 serves to keep the valve in its park position.

As a pressure sensing means, spring 293 serves to overcome unusually low pressure .in line 132 to apply the brakes by venting the line 138. Manual reset is subsequently required so as to impart an additional safety factor to its operation.

Another fluid pressure signal type system employing an actuator means controlled by receipt of fluid pressure signals and operating to counteract a bias pressure to release stored energy of springs in a braking system is shown in FIGURE 19. The system in FIGURE 19 includes a fluid pressure source including a compressor 173 supplyin position identified by the letter 1 1 ing fluid under pressure to a reservoir 174 through a check valve 175. A recirculating line 176 incorporating a governor 177 provides a return to compressor 173. A fluid shutoff means 178 is provided by a pet cock in an output line 179 leading from reservoir 174. When shutoff means 178 is disposed to disconnect reservoir 174 from primary service system elements downstream thereof a standby emergency system for limited operation of the brakes can be activated.

The emergency standby system generally includes a spare fluid pressure reservoir 180 protected by a check valve so as to form a second source of fluid under pressure when used in combination with compressor 173 and reservoir 174 or, in the event of the failure of either of the latter, can be used by itself for a limited period. Thus, when compressor 173 and reservoir 174 are fully operative, compressor 173 will serve to maintain pressure in reservoir 180 at a predetermined level via reservoir 174. Where so called wet and dry tanks are required in order to comply with motor vehicle regulations or physical system performance, reservoirs 174, 180 can be employed to meet this requirement. The standby system further includes a hand-operated valve 181 connected to vary and transmit pressure from reservoir 180 directly to the brake cylinders so as to release the brakes in a corresponding degree dependent upon manipulation of valve 181. Valve means 140 or 240 can serve this purpose when modified for hand control as by employing a hand lever rotating a camming portion to move plunger 201 as desired. A closed center three-way valve 182 is disposed immediately upstream of each brake cylinder whereby the fluid pressure line 183, can be selectively connected or disconnected to control the brake cylinder. Valve 182 can also be conditioned to selectively connect and disconnect the primary service brake system when s, as well as being able to be disposed to disconnect the brake cylinder entirely from both systems.

Operation of the primary service system of the arrangement in FIGURE 19 follows substantially along the lines of the system previously described with respect to FIG- URE 11 and accordingly it is not considered necessary to repeat that description at this time.

As noted above, emergency braking has been effected in the past, by means of spring forces which are released upon failure of the air system. I have observed that while these springs have been sufiicient to serve as parking brakes, their operation has been of such limited effectiveness that in a number of jurisdictions it has even become unlawful to refer to them as emergency brakes. I have further observed that their effectiveness is reduced by reason of requiring them to remain compressed over long periods of time, extending for example, into days and weeks. Furthermore, the flexing life of single, large sized springs as used in many emergency braking systems is relatively short. Accordingly, I have provided preferred braking means which can be operated either hydraulically or pneumatically in the above described systems, and which will provide satisfactory operation over an extended period relative to the life of the vehicle itself.

In general, the brake cylinders as designated by the reference numeral 90 in FIGURE 5, each include a cylinder, a piston movable within the cylinder, and a connecting member carried by the piston for moving the brake shoes between brake-applying and brake-releasing positions. Resilient biasing means are provided to yieldingly urge the piston with respect to the cylinder to move the connecting member.

The resilient biasing means preferably comprises a number of helical springs, each having an axis spaced from the axis of the cylinder and extending substantially parallel to the cylinder axis. The axes of the springs are spaced from each other and distributed around the cylinder axis, thereby providing a long-lived and powerful spring biasing means. A fluid receiving space is defined between one end of the cylinder and the piston and adapted to be pressurized either by hydraulic fiuid or by pneumatic means to overcome the urging of the powerful resilient biasing means. In a particularly preferred embodiment, plural banks of short, light weight helical springs are provided within the cylinder and separated by a plate which is mutually supported by the adjacent banks. Thus, the banks are arranged in tandem generally axially of the cylinder. Should any one of the springs become defective, it will have virtually no harmful effect upon the overall braking efficiency of the cylinder.

In particular, a cylinder is provided with an end cap member 92 formed with an annular skirt 93. Skirt 93 is adapted to extend coaxially into cylinder 90 and is welded at 94 to form a sealed closure. The inner surface of member 92 is formed to include a number of cylindrical seats 95 adapted to receive helical springs 96 therein.

At the other end of cylinder 90 a movable piston 97 is carried to ride on a pair of relatively widely spaced O-rings 98a, 98b, disposed around the axially extending skirt 99 of piston 97. The relatively Wide axial spacing between O-rings 98a, 98b, serves to prevent binding of piston 97 within cylinder 90. The inner end surface 100 of piston 97 is formed to provide circular seats 101 substantially aligned with corresponding seats 95. Springs 96, in the main, are distributed substantially parallel to and spaced from the axis of cylinder 90 as well as being spaced from each other. Two springs 96 are disposed coaxially of cylinder 90 and positioned in tandem. The ends of springs 96 are carried in seats 95, 101 and can (in another embodiment) extend continuously from one end to the other. However, the arrangement employing a relatively large number of springs arranged in two tandem banks extending along the axis of cylinder 90 is preferred. As noted, the two banks are separated by a plate 102 mutually supported by the springs of both banks.

Plate 102 is formed with oppositely extending boss portions 103, 104. Portions 103, 104 fit Within an end convolution of the springs to carry them respectively between boss portions 103, 104 and seats 95, 101. A cylindrically shaped opening 105 extends through plate 102 coaxially of each pair of boss portions 103, 104. With the exception of that opening 105 disposed coaxially of cylinder 90, openings 105 serve to receive cylindrical guide members 106 which are carried substantially c0- axially within springs 96 and mounted in seats 95. The peripheral edge of plate 102 carries an O-ring 107 to take up any abrasive wear which might otherwise be encountered by springs 96. Guide cylinders 106 are preferred mostly for use with long springs extending end to end in cylinder 90 when not employing plate 102. Thus, as shown, plate 102 can, if desired, be removed and longer springs be employed.

In order to reject moisture which might otherwise tend to accumulate within cylinder 90, when used as a pneumatic system, the cylindrical space defined between the inner surface of member 92 and piston 97 includes a free volume of water-rejecting lubricant, such as motor oil. It is preferred for most purposes that the amount of this free volume of oil be on the order of a quart as distinguished from slight deposits as might be used for more lubrication. Means for passing the motor oil into cylinder 90 include a filling cap 307 screwed onto an exteriorly threaded boss 120. Means for sealing, substantially 13 moisture-free, the space defined between member 92 and piston 97 from the space 100' (FIGURE defined between the piston head and the adjacent end of cylinder 90 includes in addition to the pair of spaced O-rings 98a, 9312, an encircling wick 108 of suitable absorbent material such as felt, carried in wiping engagement with the side wall of cylinder 90. Wick 108 is disposed near the trailing edge of skirt 99 so as to be interposed between the moisture-free space and O-ring 98b. Plate 102 includes fluid transfer holes 102a to insure free movement of the oil thereacross, from one side to the other.

Piston 97, as shown in FIGURE 6, is in a fully extended position. This condition normally will not exist while the cylinder is mounted on the vehicle but rather is representative of the condition of piston 97 prior to installation. In this condition, the head of piston 97 abuts the end of cylinder 90. Fluid passage means for pressurizing and later controlling piston 97 against the urging of springs 96 includes the relatively large port 109. Port 109, being relatively large, is not subject to becoming clogged with grit, dirt and the like as has been a common source of air brake problems.

Prior to installation, port 109 is connected to the compressed air supply whereby space 100 can be subjected to pressure. In order to provide suflicient active pressure receiving area to enable installation to be made, means are provided for injecting fluid under pressure, between the end surface of piston 97 and the abutting end of cylinder 90. Thus the end surface of piston 97 includes a plurality of radially extending depressions 110 providing sufficient pressure-receiving area in fluid communication with port 109 whereby sufficient force is generated to overcome the spring biasing means. With the piston partially retracted under fluid pressure, cylinders 90 can be connected up and mounted to the vehicle.

As shown in FIGURE 5, the brake shoes 117 are arranged to be moved to a brake set position by clockwise rotation of lever arm 116. A connecting member or rod 112 can be threadedly engaged in the end of piston 97 and connected at its other end in the system as shown in FIGURE 5. It should be noted that in FIGURE 5, rod 112 is arranged whereby movement to the right, i.e., pushing on rod 112, serves to move the brake shoes to brake-applying position. In this instance cylinder 90 can be mounted by studs 111. Rod 112 extends through an exteriorly threaded boss 121 which in turn carries a removable gland member 122 provided with a pair of O-rings 123 and wiper 124.

Where it is desired to move the brake shoes to brake applying position by pulling on rod 112, rather than by pushing, rod 112 can be readily removed and passed through the opposite end of cylinder 90 via 'boss 120 until it engages threads 113 in piston 97. In the latter event, cylinder 90 can be carried on the vehicle by means of a pair of radially spaced brackets 114. When brackets 114 are used to mount cylinder 90, the double-pivoted clevis 115 can be replaced by a single connecting pin inasmuch as brackets 114- serve to permit cylinder 90 to rock slightly to compensate for the arc defined by the upper end of lever arm 116.

From the foregoing description, it will be evident that failure or fatigue of any of springs 96 is easily compensated by means of plate 102. At the same time, a powerful spring force is provided while taking advantage of the longer flexing life of short, lightweight springs which can be on the order of conventional automotive valve springs.

As shown in FIGURE 10*, piston 97 moves to an intermediate position in cylinder 90 when the brake shoes are fully applied. It will be evident from the spacing between the piston head and the adjacent end of cylinder 90 that considerable throw is left in reserve. Thus, if the brake linings are entirely destroyed, the brake shoes can nevertheless be further driven if needed be, even into metal-to-metal contact with the drums whereby the shoes and drum will fuse under heat generated thereby. With this kind of throw fading is thereby virtually eliminated.

While the throw of member 112 is considerably increased, the over-all extent of cylinder remains as short or shorter than conventional units.

If it is desired to operate without benefit of plate 102 helical springs sufficiently long to extend from member 92 to the inner surface of piston 97 can replace the tandem pairs of shorter springs shown. In this event, cylindrical guides 106 serve to maintain the springs in an aligned condition whereby the springs do not interfere with one another or with the operation of piston 97.

As noted above, a commercially acceptable brake unit for the above systems must provide the flexing qualities characteristic of low force springs while developing a satisfactory spring force to actuate the brakes. This must be achieved, however, while avoiding the adverse buckling and cocking normally encountered at those convolutions located respectively either midway between, or at, the ends of the spring. It will also be recalled that the compression spring means used should provide a sufficiently long stroke to eliminate the fading problem without significantly extending the length of the brake cylinder unit beyond conventional lengths.

In providing spring biasing forces sufficient to be employed in service braking operation of a vehicle, such as a heavily laden tractor-trailer rig, spring life is obviously important. It is generally considered that compression springs, for best results should be limited to a maximum flexure of half their length for springs having a length three times their coil diameter. Thus, for a spring of two inch coil diameter a preferred length (3:1) of six inches should not be compressed in normal operation much more than three inches. Therefore, as shown above, seven springs of roughly two inch coil diameter are arranged in a single bank to generate suflicient braking force at the wheels. A second, and similar, bank of springs is added to develop a preferred rather extended throw of the piston. Additional banks can be employed to further lengthen the throw.

At this point, if additional spring force is to be developed, more powerful springs or additional springs can be used. The former will lose some of the flexing advantage of lower power springs, while the latter will either require an increased brake cylinder diameter or use of springs of a smaller coil diameter. If the springs are to be of equal length to the seven two-inch diameter springs shown, their diminished coil diameter will violate the rule of diameter to length stated above for preferred performance.

I have observed, however, that if the axis of these smaller diameter springs is closely confined during flexure whereby lateral movement of the axis is restrained, the 3:1 preferred relationship can be disregarded without adverse effect. I have further observed that as the ratio of length to coil diameter increases, the wire diameter of the spring normally will be decreased to provide further improved flexing life. Thus, in a particular-1y preferred embodiment described below, I have employed a nested helical spring construction wherein a plurality of three helical springs are concentrically disposed, the outer spring having substantially the optimum 3:1 relation of length to coil diameter. The outer spring employs a helix of opposite hand to the next adjacent inner spring and this scheme has been found to provide excellent lateral restraint such as when a close spaced sliding fit relation on the order of .010 inch is employed. The free volume of oil within the cylinder provides spring lubrication.

To further preclude lateral movement of the spring axis, a guide post is telescopically carried axially of the nested springs and supported from the divider plate. The divider plate serves, as above, to permit the axial displacement of the brake piston to be effectively doubled without detriment, such as fracture of the springs at their midpoints.

The divider plate, while supported by the helical spring arrangement on each side, is formed slightly spaced from the side wall of the cylinder to accommodate any limited tilting movement thereof caused by failure of one of the springs. At one end of the springs, the guide posts are formed with a tapered enlargement of their diameter to provide an axial seat within an end convolution of the innermost spring. A coaxial annular seat encircles the end convolution of the outermost spring. At the other end of the nested springs, an annular recessed surface and peripheral rim form a seat while a circular boss protrudes coaxially within the innermost spring.

The guide posts are sufiiciently elongated whereby, upon maximum spring compression, they will extend axially of the springs to within a slight spaced relation with respect to the boss aligned therewith thereby ensuring that the end convolutions of the springs do not become unseated or cocked at an angle as can be caused by the twist generated in spring compression movement.

The skirts of the piston and cylinder end-cap, and the outer margin of the divider plate meet when the piston is at its full spring compression position so as to define the maximum spring compression relation, and evenly relate the load between each bank, while precluding coil contact.

This general arrangement is shown in detail in the embodiment of FIGURES 14 through 17. A brake cylinder 250 is formed with a relatively thick end portion 251 to accommodate a rather large diameter fluid passage 252 for admitting fluid under pressure into the interior of cylinder 250. The other end of cylinder 250 is, as formed, open. To seal the open end of cylinder 250 an end cap 253 is welded at 254. Cap 253 is provided with a skirt 255 of equal axial extent to a skirt 256 of a movable piston 257. Piston 257 is formed with a piston rod 258 for connection to a brake actuating cam lever such as shown at 116 in the system in FIGURE 5. In order to support the brake unit in its installed position, a pair of mounting studs 259 (only the far one of which is shown) are formed in end portion 251 on opposite sides of piston rod 258.

In order to provide breathing for that portion of the interior of cylinder 250 that is defined between skirts 255 and 256, a fluid passage fitting 261 is provided coaxially of end cap 253. As noted above, the interior of cylinder 250 carries a small deposit of Water-repellant lubricant and this lubricant can therefore, be injected into the cylinder via fitting 261.

The divider plate 262 is formed at its periphery to receive an O-ring whereby plate 262 moves axially along the cylinder with a loose fit, on the order of a sixteenth inch radial clearance to accommodate a slight tilt if a spring should fail. Plate 262 carries a plurality of guide posts 263 of preferably solid construction from end to end. Posts 263 are formed at their midpoint with a tapered enlargement 264 of their diameters to snugly receive the end convolution of the innermost helical spring 265.

A nested arrangement of three springs 265, 266 and 267 is slidably supported around each of the seven guide posts 263. In the drawings, for sake of clarity and simplicity of illustration, only a pair of nested tandemly aligned springs so arranged has been shown. The helix of the innermost and outermost springs, respectively 265, 267, is of the same hand whereas the helix of spring 266 is of an opposite hand whereby entanglement of adjacent springs is precluded and smooth sleeve-like guidance of each spring achieved. The coils of springs 265- 267 are radially spaced from one another to provide a slight sliding clearance on the order of .010 inch, thereby restraining lateral movement of their common axis. The free volume of lubricant in the cylinder aids relative axial movement therebetween.

At the ends of the outermost springs 267 located remote from plate 262 an annular seat is provided to encircle the end convolution of the spring to ensure that the end convolution of the springs will not become unseated or cocked at an angle under the twisting movement generated by spring compression. Thus the annular seat includes a protruding boss 268 axially aligned with its respective guide post 263. A recessed annular surface 269 encircles boss 268 and the outer periphery of surface 269 is formed to include an axially extending rim portion 270.

Guide posts 263 are sufliciently elongated whereby upon maximum spring compression as defined by abutment between skirts 255, 256 with the peripheral margin of plate 262, a slight spacing 271 (FIGURE 17) serves to prevent the springs from becoming 'unseated during operation of the brake cylinder. Spacing 271 can preferably be on the order of one or two thicknesses or less of the wire diameter of the innermost spring.

Divider plate 262 is further provided with fluid passages or ports 272 for equalizing the transfer of fluid between each side of plate 262.

As shown in FIGURE 14 the piston head 257 is adapted to abut the inner end surface of cylinder 250. This condition, while normally not existing during operation of the brake unit, will exist prior to installation of the brake unit on a vehicle. Accordingly, at the time of installation it will be necessary to inject fluid pressure between the inner end of cylinder 250 and piston 257. The pressure must be suflicient to develop a force which will overcome the biasing force of the springs within the cylinder. The pressure-receiving surface of piston 257 which is adapted to abut the inner end of cylinder 250 is therefore formed to include alternately raised and relieved areas closely spaced to uniformly distribute the loading of the spring biasing forces acting against the piston head from the other side when the head is in its abutting condition.

Uniform distribution of these spring forces generally across the entire face of piston 257 is necessary to prevent cracking or distortion of the piston head, as will be readily apparent when it is considered that somewhere on the order of 4200 pounds of force is developed by springs employed in the embodiment shown in FIGURE 14.

This force can be developed using a spring 267 developing 300 pounds of force, a spring 266 developing 200 pounds of force, and a spring 265 developing pounds of force. The spacing and extent of the surface areas provided by raised portions 274 must not, however, preempt the provision of a sufiiciently large pressure receiving area formed by the recessed portions 275 which are in fluid communication with the fluid passage 252 so as to receive fluid pressure and develop a force which can overpower the force of the spring biasing means. Accordingly the arrangement shown in FIGURE 15 has proven satisfactory for accommodating both of these foregoing requirements.

Simpler embodiments of the above construction are shown in FIGURES 20 and 21. In FIGURE 20, for example, there is shown a brake unit of the above described kind wherein spring forces are employed to drive a piston to brake applying position which includes a plurality of helical springs 280, 281 disposed in concentric closely spaced relation, wherein the helices of the adjacent springs are of opposite hand to each other and the spaced relation between the springs measured radially thereof is sufliciently close whereby the outer spring serves to guide and confine the adjacent spring movement sub stantially to axial movement thereof. It will also be observed that posts 282, 283 are axially aligned coaxially of springs 280, 281 and are elongated to provide a close spaced relation at their ends. Vent 284 provides breathing.

As shown in the embodiment of FIGURE 21 a brake cylinder unit of simplified construction includes a single helical spring 285 having a powerful spring constant and a guiding divider plate. Thus, helical spring means act axially of the cylinder and are disposed around cylindri- 117 cally shaped guide means 286 extending a substantial distance along the cylinder concentrically of and closely spaced from the helical springs 235 so as to slidably confine the axis of springs 285 and substantially preclude lateral movement thereof during longitudinal movement of the piston 287.

From the foregoing it will be evident that a system of the above kind, made feasible by the actuating units described, will have a number of operating advantages as previously noted.

What is claimed is:

l. A brake system adapted to be carried by a motor vehicle comprising a cam shaft effective to actuate a brake shoe in a first direction of angular shaft rotation and to release a brake shoe in a second direction of angular shaft rotation, biasing means connected to said cam shaft for resiliently urging said cam shaft in said first direction, fluid pressure means connected to said cam shaft for overcoming said biasing means whereby said cam shaft is rotated in said second direction, pressure source means for supplying fluid under pressure to said fluid pressure means, means forming a fluid supply line path connecting the source means and said fluid pressure means, and valve means controlled by the operator of the motor vehicle for both service and emergency operation, said valve means being capable of selectively supplying fluid under pressure from said fluid supply source means to said fluid pressure means and subsequently selectively removing fluid from said fluid pressure means, said valve means being normally operatively responsive to fluid under pressure from said source serving to operate said valve means to normally condition said path to transmit pressure to said fluid pressure means and rotate said cam shaft in said second direction, and further operatively responsive to selec tively apply a counteracting fluid pressure from said source to condition said path to remove fluid from said fluid pressure means and rotate said cam shaft in said first direction.

2. The brake system of claim 1 wherein said fluid pressure means includes a cylinder, a plunger having a piston head reciprocably mounted in said cylinder, said plunger projecting beyond one end of said cylinder and terminating in a clevis, a first pair of fluid inlet and fluid outlet lines connected to the interior of said cylinder on the other end of said cylinder; a second pair of fluid inlet and fluid outlet lines connected to said interior on said other end; valve means connected to said first pair and said second pair of fluid lines for selectively and oppositely opening and closing each of said pairs of lines, and a lever connecting said clevis and said cam shaft whereby said cam shaft is rotated in dependence upon the position of said plunger within said cylinder.

3. The device of claim 2 wherein said cam shaft biasing means includes a compression spring disposed within said cylinder between said piston head and said one end of said cylinder, said spring acting to bias said head away from said one end of said cylinder whereby said cam shaft is biased in said first direction of angular rotation.

4. In a brake system adapted to be carried by a wheeled vehicle carrying a brake drum having a friction surface, a coacting brake shoe carrying a lining arranged for movement into and out of engagement with the friction surface to apply and release the brakes, brake actuating apparatus comprising a member connected to move said shoe between brake applying and brake releasing positions, a cylinder, a piston movable within the cylinder to move the member, spring biasing means disposed to resiliently urge said piston with respect to said cylinder and permitted to move said member to brake applying position for both service and emergency operation, the energy for moving said member to brake applying position during both service and emergency operation being derived substantially entirely by releasing stored energy from said spring biasing means, a fluid pressure system l 8 including a source of fluid under pressure, first valve means disposed between said source and said cylinder and operable in one condition to transmit a fluid pressure into said cylinder to the face of said piston suflicient to overpower said spring biasing means and operable in another condition to vent fluid pressure from said cylinder to release stored energy of said spring biasing means, means under pressure of said source providing a biasing fluid pressure, an actuator responsive to and normally disposed in a given direction by said biasing fluid pressure so as to be normally acting to condition said first valve means fully to said first named condition, a fluid inlet for introducing a selected counteracting fluid pressure to said actuator to operate said actuator in a direction opposite to said given direction to condition said first valve means in varying degree to said second named condition, second valve means operable from the operators compartment of the vehicle for both gradually and substantially instantaneously directing one of a range of fluid pressures from said source to said inlet to operate said actuator in a corresponding varying degree.

5. Brake system apparatus according to claim 4 wherein the first named source of fluid under pressure includes a fluid pressure reservoir disposed to supply fluid under pressure to said first valve means, said source further including a compressor, and check valve means interposed between said fluid pressure reservoir and said compressor to retain pressure in said reservoir upon failure of said compressor.

6. Brake system apparatus as defined in claim 4 further including a plurality of said cylinders each being associated with a respective one of the wheels of a vehicle and wherein said source further includes compressor means and a first fluid pressure reservoir and fluid shutoff means serving to selectively isolate said source from the remainder of said fluid pressure system and wherein there is further included a standby system for limited postemergency use comprising a second source of fluid under pressure, said second source including a second fluid pressure reservoir connected to be maintained at a predetermined pressure by supply from said compressor means, a hand-operated valve connected to vary and transmit pressure from said second reservoir to said brake cylinder to release the brakes in corresponding degree, and individual valve means respectively associated with each of said cylinders, each of said individual valve means serving to selectively connect and disconnect said handoperated valve with respect to its associated one of said cylinder or to connect and disconnect said first valve means with respect to its said associated cylinder.

7. Brake system apparatus according to claim 6 wherein the individual valve means which serve to selectively connect and disconnect said hand-operated valve with respect to their associated ones of said cylinders or to connect and disconnect said first valve means with respect to said cylinders is each disposed immediately upstream of its associated respective one of said cylinders.

8. For operating a vehicular brake actuator unit including a cylinder, a piston Within the cylinder movable between brake applying and releasing positions, spring means serving to move the piston to brake applying position for both service and emergency operation, and a source of fluid under pressure to be supplied to said cylinder to move said piston to brake releasing position, a fluid pressure system for operating said piston comprising first valve means coupled to said source for varying the pressure in said cylinder to release, in a selected degree, stored energy in said spring means or to restore same, valve actuating means including plunger means under pressure of said source serving normally to move said plunger means in a first direction to condition said first valve means to maintain said spring means fully restored, an inlet for applying to said plunger a counteracting signal pressure from said source serving to variably resist the movement of said plunger means in said first direction both to partially or fully release said stored energy, second valve means operable from the operators compartment of the vehicle serving to supply said signal pressure from said source in varying degree to said inlet to correspondingly vary the movement of said plunger means in said first direction to variably release the stored energy of said spring means.

9. Apparatus of the kind defined in claim 8 wherein said plunger means comprises first and second expansible pressure chambers, each having a movable wall, said walls being of different pressure receiving areas and movable as a unitary construction between advanced and retracted positions, the pressure receiving area of the movable wall of the first chamber being the lesser, an actuator member movable with said walls, and fluid passage means normally passing fluid pressure of said source into said first chamber to urge said walls and said actuator member to said advanced position, said inlet for applying a counteracting signal pressure being disposed to pass fluid pressure from said source into said second chamber under control of said second valve means to urge said walls toward their retracted position.

10. Brake apparatus according to claim 9 wherein said expansible chambers are formed by cylinders of different cross sectional areas, each cylinder including a piston head sealing adjacent ends of the cylinders and defining a dead air space therebetween, the heads being fixed to each other to move as a unitary construction and defining a dead air space therebetween, and fluid passage means disposed to pass lubricant into and out of said space, and, during movement of said piston heads, to vent said space.

11. In a brake system adapted to be carried by a wheeled vehicle carrying a brake drum having a friction surface, a coacting brake shoe carrying a lining arranged for movement into and out of engagement with the friction surface to apply and release the brakes, brake actuating apparatus comprising a member connected to move said shoe between brake applying and brake releasing positions, a cylinder, a piston movable within the cylinder to move the member, spring biasing means disposed to resiliently urge said piston with respect to said cylinder and permitted to move said member to brake applying position for both service and emergency operation, the energy for moving said member to brake applying position during both service and emergency operation being derived substantially entirely by releasing stored energy from said spring biasing means, a fluid pressure system including a source of fluid under pressure, first valve means disposed between said source and said cylinder and operable in one condition to transmit a fluid pressure into said cylinder to the face of said piston suflicient to overpower said spring biasing means and operable in another condition to vent fluid pressure from said cylinder to release stored energy of said spring biasing means, means providing a biasing fluid pressure, an actuator responsive to and disposed by said biasing fluid pressure so as to be normally acting to condition said first valve means fully to said first named condition, a fluid inlet for introducing a selected counteracting fluid pressure to said actuator to operate said first valve means in varying degree to said second named condition, second valve means operable from the operators compartment of the vehicle for both gradually and substantially instantaneously directing one of a range of fluid pressures from said source to said inlet to operate said actuator in a corresponding varying degree, a large capacity valve upstream of said actuator and operable from the cab of the vehicle serving, in service operating condition, to transmit said bias ing fluid pressure to said actuator and, in parking condition, to quickly relieve to atmospheric said biasing fluid pressure from said actuator, said large capacity valve further including means for holding same in its said parking condition, and resilient means urging said actuator to that condition thereof for venting fluid pressure from said cylinder to release the stored energy of the brake applying springs whereby reapplication of said biasing fluid pressure is dependent upon manual resetting of said valve to said service operating condition, thereby providing a parking brake.

12. Brake system apparatus as in claim 11 wherein said large capacity valve is responsively connected in the fluid bias line to sense unusual loss of pressure in said fluid pressure source and automatically shift to said parking condition to provide emergency application of said brakes by venting said bias pressure while requiring manual resetting of the valve to said service condition following the emergency.

13. Brake system apparatus as in claim 12 wherein said large capacity valve is manually operable between first and second positions respectively either transmitting said biasing fluid pressure to said actuator to condition same to brake releasing condition, or venting said biasing fluid pressure to atmospheric to condition said actuator to brake applying condition, a bleed connection disposed to direct fluid pressure of said source to yieldingly hold said large capacity valve in its said first position, and resilient means disposed to provide a countervailing force acting against the yieldingly holding force, said countervailing force being normally insuflicient to move said large capacity valve to its said second position, the force of said resilient means being sufficient to overcome the yieldingly holding force upon occasion of unusual pressure drop at said bleed connection to automatically shift said valve to its second position, and said valve being formed and disposed to block said bleed connection when moved to the second position to permit said resilient means to retain said valve thereat until manually reset.

14. A brake system adapted to be carried by a wheeled vehicle employing a brake drum having a friction surface, a coacting brake shoe and lining arranged for movement into and out of engagement with the friction surface to apply and release the brakes, said brake system including brake actuating apparatus comprising a member connected to move said shoe between brake applying and brake releasing positions, a cylinder, a piston movable within the cylinder to move the member, spring biasing means disposed to resiliently urge said piston with respect to said cylinder and permit it to move said member to brake applying position for both service and emergency operation, the energy for moving said member to brake applying position during both service and emergency operation being derived substantially entirely by releasing stored energy from said spring biasing means, a source of fluid under pressure, valve means operable from the operators compartment of the vehicle for both gradually and substantially instantaneously directing one of a range of fluid pressures from said source to said cylinder to operate said piston in a corresponding varying degree, and a large capacity valve manually operable between first and second positions respectively either transmitting said fluid pressure to said cylinder to condition said piston to brake releasing condition, or venting said fluid pressure to atmospheric to condition said piston to brake applying condition, a bleed connection disposed to direct fluid pressure of said source to yieldingly hold said large capacity valve in its said first position and resilient means disposed to provide a countervailing force acting against the yieldingly holding force, said countervailing force being normally insufficient to move said large capacity valve to its second position, the force of said resilient means being suflicient to overcome the yieldingly holding force upon occasion of unusual pressure drop at said bleed connection to automatically shift said valve to its second position, and said valve being formed and disposed to block said bleed connection when moved to the second position to permit said resilient means to retain said valve thereat until manually reset.

(References on following page) References Cited by the Examiner UNITED STATES PATENTS Stout et a1 188170 X Schnell 188-170 X Weiland 188-170 X Cambeis 3034O X Kohler 303-13 X Casey 30371 EUGENE G. BOTZ, Primary Examiner. 

1. A BRAKE SYSTEM ADAPTED TO BE CARRIED BY A MOTOR VEHICLE COMPRISING A CAM SHAFT EFFECTIVE TO ACTUATE A BRAKE SHOE IN A FIRST DIRECTION OF ANGULAR SHAFT ROTATION AND TO RELEASE A BRAKE SHOE IN A SECOND DIRECTION OF ANGULAR SHAFT ROTATION, BIASING MEANS CONNECTED TO SAID CAM SHAFT FOR RESILIENTLY URGING SAID CAM SHAFT IN SAID FIRST DIRECTION, FLUID PRESSURE MEANS CONNECTED TO SAID CAM SHAFT FOR OVERCOMING SAID BIASING MEANS WHEREBY SAID CAM SHAFT IS ROTATED IN SAID SECOND DIRECTION, PRESSURE SOURCE MEANS FOR SUPPLYING FLUID UNDER PRESSURE TO SAID FLUID PRESSURE MEANS, MEANS FORMING A FLUID SUPPLY LINE PATH CONNECTING THE SOURCE MEANS AND SAID FLUID PRESSURE MEANS, AND VALVE MEANS CONTROLLED BY THE OPERATOR OF THE MOTOR VEHICLE FOR BOTH SERVICE AND EMERGENCY OPERATION, SAID VALVE MEANS BEING CAPABLE OF SELECTIVELY SUPPLYING FLUID UNDER PRESSURE FROM SAID FLUID SUPPLY SOURCE MEANS TO SAID FLUID PRESSURE MEANS AND SUBSEQUENTLY SELECTIVELY REMOVING FLUID FROM SAID FLUID PRESSURE MEANS, SAID VALVE MEANS BEING NORMALLY 